Funding for this research was provided by:
National Health and Family Planning Commission of the People's Republic of China (entrusted by National Health and Family Planning Commission of the People's Republic of China)
Received: 5 February 2019
Accepted: 9 May 2019
First Online: 14 May 2019
Ethics approval and consent to participate
: The Ethics Committee of China Medical University approved the study protocol. This analysis used secondary data, and the authors did not require direct contact with participants, thus informed consent was not applicable.
: Not applicable.
: The authors declare that they have no competing interests.
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